Atlas de Especies Invasoras de Puerto Rico

Non-natives: 141 scientist object

We the undersigned feel that in advocating a change in the environmental management of introduced species (Nature 474, 153–154; 2011), Mark Davis and colleagues assail two straw men.

First, most conservation biologists and ecologists do not oppose non-native species per se — only those targeted by the Convention on Biological Diversity as threatening “ecosystems, habitats or species”. There is no campaign against all introductions: scarcity of resources forces managers to prioritize according to the impact of troublesome species, as in the Australian Weed Risk Assessment.

Second, invasion biologists and managers do not ignore the benefits of introduced species. They recognize that many non-native species curtail erosion and provide food, timber and other services. Nobody tries to eradicate wheat, for instance. Useful non-native species may sometimes still need to be managed because they have a negative impact, such as tree invasions that cause water loss in the South African fynbos.

Davis and colleagues downplay the severe impact of non-native species that may not manifest for decades after their introduction — as occurred with the Brazilian pepper shrub (Schinus terebinthifolius) in Florida (J. J. Ewel in Ecology of Biological Invasions of North America and Hawaii (eds H. A. Mooney and J. A. Drake)214–230; Springer, 1986). Also, some species may have only a subtle immediate impact but affect entire ecosystems, for example through their effect on soils.

Pronouncing a newly introduced species as harmless can lead to bad decisions about its management. A species added to a plant community that has no evolutionary experience of that organism should be carefully watched.

For some introductions, eradication is possible. For example, 27 invasive species have been eradicated from the Galapagos Islands, mitigating severe adverse effects on endemic species. Harmful invasive species have been successfully kept in check by biological, chemical and mechanical means.

The public must be vigilant of introductions and continue to support the many successful management efforts.